Collaborative GA-PIRSA-NTGS-GSWA studies with … · Collaborative GA-PIRSA-NTGS-GSWA studies with...

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Presentation Notes�

Collaborative GA-PIRSA-NTGS-GSWA studies with important contributions from: Primary Industries and Resources of South Australia Northern Territory Geological Survey Geological Survey of Western Australia �

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The major messages from the presentation are: (1) the diversity of Ni sulphide mineralisation through geological time, from the Archaean to the Phanerozoic; and (2) the considerable potential for the discovery of further deposits in Australia, particularly under shallow cover. �

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Australia is well endowed with both Ni sulphide and lateritic deposits. World-class deposits include: Kambalda, Mount Keith, Leinster, and Murrin Murrin. World Ni sulphide production has historically been dominated by the Noril’sk (Russia) and Sudbury (Canada) deposits. Significant new Ni sulphide developments include: Voisey’s Bay, Canada (to commence production ~2006) and Kabanga, northwest Tanzania (resource under review). Elias, M., 2002. Nickel laterite deposits-geological overview, resources and exploitation, in Giant Ore Deposits: Characteristics, Genesis, and Exploration, Cooke, D.R., Pongratz, J., eds, Centre for Ore Deposit Research Special Publication 4. Univ. of Tasmania, 205–220.�

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Massive Ni-Cu-Co sulphide ores are important to the economic status of most Ni deposits associated with mafic-ultramafic igneous rocks. Deposits associated with komatiitic rocks (Kambalda-type) and tholeiitic mafic intrusions (Radio Hill, Sally Malay) are generally dependent on the accumulation of massive sulphides to be economic. However, some low-grade disseminated sulphide deposits (Mount Keith-type) can be economic by virtue of their large size. Massive sulphides from three major deposits in the world (left) are compared with three Australian examples (right). Radio Hill and Sally Malay are economic deposits associated with Precambrian layered mafic intrusions and Honeymoon Well is an Archaean komatiite deposit. Minerals shown are: yellow = chalcopyrite; cream to pale yellow = pentlandite; grey to pale brown = pyrrhotite; large highly reflective cubic crystal near centre of chalcopyrite-bornite ore from Noril’sk (example 3) = sperrylite (Pt arsenide); and black = gangue. �

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Exploration for Ni sulphides in Australia has had several successes in recent years. These include both komatiite- and mafic intrusion-type settings, particularly in poorly-exposed Archaean and Proterozoic provinces. Recent exploration has been stimulated by the discovery of new deposits (Flying Fox, Daybreak, Armstrong, Daltons, McEwen, Nebo-Babel; all Western Australia), recognition of different styles of mineralisation (Avebury, Tasmania), and the protracted period of elevated metal prices, e.g., four-fold increase in Ni over the last 2 years and significant price increases in other metals commonly associated with Ni, such as Pt and �

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Australian Ni production is dominated by Archaean komatiite deposits (82%) followed by laterite deposits (15%); both these deposit types are most abundant in the Archaean Yilgarn Craton of Western Australia. However, Ni resources are dominated by laterite deposits (69%), with komatiite deposits hosting less than 30% of Australia’s total Ni resources. Mafic intrusions account for only a few per cent of Ni production and resources. �

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Plot of Ni grade (wt%) versus global resources of ore (production and total resources in million tonnes) for the major Ni sulphide deposits of the world. Australian deposits are shown with filled symbols and non-Australian deposits with open symbols. Diagonal lines show contained Ni metal in tonnes and the region enclosed by the green dashed line corresponds to the major Ni laterite deposits of the world. Source of data: Australian deposits – OZMIN (GA's database of mineral deposits and resources); non-Australian sulphide deposits – Naldrett (2002); and laterite field – Elias (2002). The grade-tonnage Ni comparisons highlight that Australia's komatiite- and laterite-associated deposits contain similar amounts of metal relative to similar world-class deposits, but deposits hosted by mafic-ultramafic intrusions, although of similar grade, are of ~two orders of magnitude smaller in tonnage relative to the largest deposits. Komatiite deposits in the Yilgarn Craton of Western Australia represent some of the highest grade Ni deposits in the world, e.g., Cosmos at ~8% Ni. Elias, M., 2002. Nickel laterite deposits-geological overview, resources and exploitation, in Giant Ore Deposits: Characteristics, Genesis, and Exploration, Cooke, D.R., Pongratz, J., eds, Centre for Ore Deposit Research Special Publication 4. Univ. of Tasmania, 205–220. Naldrett A.J., 2002. Requirements for forming giant Ni-Cu sulfide deposits, in Giant Ore Deposits: Characteristics, Genesis, and Exploration, Cooke, D.R., Pongratz, J., eds, Centre for Ore Deposit Research Special Publication 4. Univ. of Tasmania, 195–204.�

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Western and central Australia showing the distributions of outcropping Precambrian mafic-ultramafic rocks, sulphide and lateritic Ni deposits, and locations of Ni sulphide deposits/prospects discussed in this presentation. Inset map shows the location of the Avebury Ni deposit in western Tasmania. �

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Archaean komatiitic rocks in the Yilgarn Craton form north-northwest-trending, laterally extensive sinuous bodies in close spatial association with mafic rocks (dominantly basalts). Nickel sulphide deposits associated with komatiites are concentrated between Kambalda and Wiluna in the Eastern Goldfields Province, and further west in the Forrestania region of the Southern Cross Province. There is considerable potential for finding further komatiite sequences along strike from known komatiites, particularly under shallow cover. �

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Cumulative frequency curves for komatiite-associated Ni deposits (contained Ni) in the Eastern Goldfields and Southern Cross provinces. Both provinces show similar distributions for small- to medium-sized deposits, however, the Southern Cross Province does not contain any ‘world-class’ (>1-2 Mt Ni) deposits. Are these large deposits absent or under cover in this province? �

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U-Pb zircon geochronology of komatiite sequences from the Yilgarn Craton show that the mineralised komatiites (2.71-2.70 Ga) in the Eastern Goldfields Province are bordered by older komatiites in the Northeastern Goldfields (>2.9 Ga) and Southern Cross (3.03-2.72 Ga) provinces. Komatiites in the younger South West (2.70-2.60 Ga) and Murchison (3.0-2.75 Ga) provinces appear to be poorly mineralised relative to the other provinces. From this dataset, the optimal time period for mineralised komatiites in the Yilgarn Craton appears to be ~2.70 to 3.03 Ga. �

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Schematic plan section of an inflationary komatiite flow showing various volcanic facies and associated Kambalda (massive sulphide ore at base of flow in preferred lava pathway) and Mt Keith (disseminated sulphide ore in centre of large olivine cumulate body) type deposits. Dowling, S.E., and Hill, R.E.T., 1998. Komatiite-hosted nickel sulphide deposits, Australia: Special Jubilee Issue of Australian Geological Survey Organisation Journal, v. 17(4), 121–127.�

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Three dimensional geometry of the Kambalda Dome highlighting the long sinuous nature of massive Ni ore shoots at the base of komatiite flows. The ore-bearing facies (channel flows) appear to anastomose and merge with one and other �

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Location of the Harris Greenstone Sequence in the central Gawler Craton, South Australia. The distribution of the greenstones is based on the interpretation of airborne magnetics, gravity, and diamond drill core. Locations of major goldfields and diamond drill holes are also shown. Inset photograph shows typical flat landscape of the Gawler Craton.�

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Generalised schematic stratigraphic profile of a single komatiite flow showing major volcanic facies, mineral and alteration assemblages, geochemical trends, and geophysical properties (incorporating DDH data from Lake Harris and Mullina Well). Such flows can be from a couple of metres thick up to ~80 m thick. Rocks shown include: (1) spinifex-textured high-Mg komatiite; (2) flow-top komatiite breccia; (3) olivine orthocumulate; (4) banded iron formation; and (5) pillowed metabasalt.�

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Comparison of whole-rock Mg contents and olivine compositions for the Lake Harris Komatiite (DDHs Lake Harris 1-2 and TAR 90-92) with the Kambalda Komatiite. The idealised cross section of the mineralised komatiite sequence shows the concentration of massive sulphides in a structural/thermal embayment along the basal contact of a channel-flow facies of the flow. Lesher, C.M., 1989. Komatiite-associated nickel sulfide deposits, in Whitney, J.A., and Naldrett, A.J., eds., Ore deposition associated with magmas. Reviews in Economic Geology, v. 4, 45–101.�

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Figure left: Fractionation S-saturation diagram showing variations of Ni versus MgO (wt%) for cumulate and ?melt-like’ (spinifex-textured) komatiitic rocks. The curves represent the fractionation of komatiitic magma containing 32% MgO and 1650 ppm Ni under S-undersaturated conditions, and under S-saturated conditions with silicate/sulphide ratios of 200 and 50, respectively. These ratios indicate the amount of olivine/sulphide separating from the fractionating magma. The curves are modified from Naldrett (1989). Most Lake Harris komatiitic samples fall along the S-undersaturated curve, with some low-Mg komatiites in DDH TAR 90 having anomalously high Ni contents due to possible remobilisation of sulphides. Figure right: Comparison of the Lake Harris data with 'melt-like' komatiite rocks from other greenstone belts (see references in Naldrett, 1989). These figures highlight that the komatiitic rocks at Lake Harris are largely S undersaturated and that the primitive flows did not assimilate significant amounts of crustal S during their evolution. This is also indicated by elevated abundances of Pt and Pd (up to 70 ppb) in these rocks. One of the major challenges for exploration companies is therefore to identify a trigger or mechanism for S saturation of these ‘fertile’ magmas, such as a S-bearing sedimentary substrate to the flows. Naldrett, A.J., 1989. Magmatic sulfide deposits. Clarendon Press, New York, 177 pp. Hoatson, D.M., Sun,S-s., Duggan, M.B., Davies, M.B., Daly, S.J., and Purvis, A.C. (in review, 2004). Physical volcanology and fertility of the Late Archaean Lake Harris Komatiite, central Gawler Craton, South Australia. Economic Geology.�

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Distribution of Palaeoproterozoic mafic-ultramafic intrusions in the Halls Creek Orogen, East Kimberley, northern Western Australia (Hoatson and Blake, 2000). The intrusions are confined to the central part of the Halls Creek Orogen, a well-exposed north-northeasterly-trending orogenic belt about 400 km long and at least 120 km wide along the southeastern margin of the Kimberley Basin. The orogen comprises low- to high-grade metasedimentary and metavolcanic rocks, and voluminous granitic, mafic, and mafic–ultramafic intrusions that collectively range in age from about 1920 Ma to 1800 Ma. Two northeast-trending parallel metallogenic corridors containing mineralised intrusions are shown as green (Ni-Cu-Co sulphides) and mauve (Cr-PGEs) zones. These two corridors have assisted mining companies in focussing their exploration activities. The Sally Malay (Ni-Cu-Co) and Panton (Cr-PGEs) intrusions are the type examples of mineralised bodies in both corridors, and are the most intensively explored intrusions in the East Kimberley. The Sally Malay deposit is planned to commence production in 2004. The Sally Malay and McIntosh intrusions discussed in this presentation are indicated on the map. Hoatson, D.M., and Blake D.H. (editors), 2000. Geology and economic potential of the Palaeoproterozoic layered mafic-ultramafic intrusions in the East Kimberley, Western Australia. Australian Geological Survey Organisation Bulletin 246, 496 pp.�

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Geological map of the mineralised Sally Malay mafic-ultramafic intrusion, East Kimberley, Western Australia. This multi-chambered intrusion consists of a primitive arcuate feeder zone (A) with overlying more evolved ovoid-shaped chambers (B, C, and D). Massive and disseminated Ni-Cu-Co sulphides are concentrated at the basal contact of the interpreted feeder zone. The rock types and geometry of the feeder conduit with associated chambers show similarities with the Voisey’s Bay Ni-Cu deposit in Canada.�

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Schematic diagram of megacyclic units and different mineralisation styles in subchamber A (interpreted feeder conduit) of the Sally Malay intrusion. Massive sulphides are concentrated in the basal keel of the chamber and are hosted by thin marginal gabbroic rocks to an overlying cyclic sequence comprising peridotite, troctolite, gabbro, and anorthosite. Some sulphides are remobilised in country rocks. Modified after Thornett (1981). Thornett, J.R., 1981. The Sally Malay deposit: gabbroid associated nickel-copper sulfide mineralization in the Halls Creek Mobile Zone, Western Australia. Economic Geology, v. 76 (6), 1565–1580.�

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Aerial photograph looking south of the McIntosh layered mafic intrusion, East Kimberley, Western Australia. This intrusion is one of the most striking landforms in the Halls Creek Orogen that is readily visible on satellite and geophysical images. The distinctive concentric pattern of alternating ridges and valleys is due to differential erosion of macrocyclic units—valleys generally correspond to olivine-rich cumulates (troctolite, rare peridotite), and ridges up to 170 m-high are composed of pyroxene-bearing mafic cumulates (olivine gabbro, olivine gabbronorite, gabbro, and magnetite gabbro). Photograph by Ian Oswald-Jacobs Aerial Photography Pty Ltd.�

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Geological map of the McIntosh mafic intrusion and nearby mafic-ultramafic intrusions in the East Kimberley, Western Australia. The 1830 ± 3 Ma McIntosh intrusion is a steep-sided, funnel-shaped body, comprising a northern ovoid part (‘cross-section of an onion’) and a southern more primitive part that narrows into a keel-shaped dyke-like body (‘ice-cream cone’). The large size (outcrop area of 85 km2 and 8 km-thick), cyclic distribution of rock types (i.e., regular magma replenishment in chamber), and S-saturated character of mafic cumulates (average ~560 ppm S) make the McIntosh intrusion a prime target for the accumulation of massive sulphides in favourable mineralised settings, such as embayments in basal contacts and in feeder conduits. Several nearby Ni-Cu-Co sulphide prospects/deposits (currently under review) in mafic-ultramafic rocks to the east and northeast of the intrusion (Eileen Bore, Salk, Copernicus, Kepler, etc) may be related to the McIntosh intrusion. �

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Aerial photograph looking north of the Radio Hill mafic-ultramafic intrusion, west Pilbara Craton, Western Australia. The Pilbara Craton is an elongate east-west-trending Archaean (~3.5-2.45 Ga) terrane comprising ovoid granitic batholiths separated by synclinal belts of metasediments and metavolcanics. Small to large layered mafic-ultramafic intrusions are prominent in the western part of the craton.�

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The Radio Hill intrusion is a small differentiated mafic body comprising a lower thin ultramafic zone overlain by two thicker gabbroic zones. Ni-Cu-Co-PGE mineralisation occurs near the lower contact of a poorly exposed ultramafic sequence with basement metavolcanics in the northwest of the intrusion. The deposit has been intermittently mined over the last decade. Inset: geology of the Radio Hill Intrusion (after Hoatson et al., 1992). Hoatson, D.M., Wallace, D.A., Sun, S-s., Macias, L.F., Simpson, C.J., and Keays, R.R., 1992. Petrology and platinum-group-element geochemistry of Archaean layered mafic-ultramafic intrusions, west Pilbara Block, Western Australia. Australian Geological Survey Organisation Bulletin 242, 320 pp.�

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Diamond drill hole section of the mineralised basal contact of the Radio Hill Intrusion. Massive and disseminated Ni-Cu-Co-PGE sulphides form thin lenses concentrated in depressions along the basal contact below the thickest sequence of overlying cumulates and in a recently defined feeder conduit. Underground mining of the deposit is planned to re-commence in 2004.�

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The Nebo and Babel Ni-Cu-Co prospects in the West Musgrave Block of central Australia created a major tenement rush in mid-2000 when WMC Resources Ltd announced significant intersections of massive and disseminated Ni-Cu-Co sulphides. The Musgrave Block is a Proterozoic metamorphic-igneous province containing several large layered mafic and mafic-ultramafic intrusions belonging to the ~1080 Ma Giles Complex. The Nebo and Babel prospects are associated with largely gabbroic rocks and are currently under review; a resource has yet to be announced. �

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Massive Ni-Cu-Co sulphides are concentrated in an interpreted moderately plunging mafic feeder conduit that supplied magma to an overlying chamber(s). Significant intersections of massive Ni-Cu-Co-PGE sulphides at the Nebo Prospect are believed to be the same mineralising environment/event as disseminated sulphides at the nearby Babel Prospect.�

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Metal contents and metal ratios of massive sulphides are very similar for the Nebo (Musgrave Block, Western Australia), Radio Hill (Pilbara Craton, Western Australia), and Voisey’s Bay (Canada) Ni-Cu-Co sulphide deposits. This indicates similar mineralising magmatic systems involving: ‘tholeiitic’ mafic intrusions; concentration of massive sulphides in embayments of basal contacts and/or in feeder conduits; dynamic emplacement of magma(s) in feeder conduits; interaction of magma(s) with country rocks and crustal contamination processes.�

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Outcrop map of the Arunta Region of central Australia. The Arunta Region is a multiply deformed and metamorphosed Precambrian-Palaeozoic basement terrane covering ~200 000 km2 in central Australia. It forms the southern part of the North Australian Craton and differs from other Proterozoic provinces of northern Australia by the marked intensity and frequency of its deformation, the high grade of much of its metamorphism, and its abundance of granite. The map highlights the wide distribution of the Proterozoic mafic intrusions and the large areas covered by alluvium. The Andrew Young Hills Intrusion in the west Arunta is featured in this presentation. �

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Geological map of the Andrew Young Hills Intrusion. Mafic rocks dominate the exposed parts (6 km of strike extent) of this large intrusion. �

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The field photographs (Hoatson & Stewart, 2001) highlight commingling of mafic and felsic magmas, e.g., mafic pillows with cuspate and contaminated margins enclosed in fine-grained granite, and resorbed alkali feldspar xenocrysts in hybrid tonalite. Such magma mixing processes may be important for inducing S saturation in the evolving mafic magma(s). Hoatson, D.M., and Stewart, A.J., 2001. Field investigations of Proterozoic mafic-ultramafic intrusions in the Arunta Province, central Australia. Canberra, Geoscience Australia Record 2001/39, 87 pp.�

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The mineral potential of the Arunta intrusions can be broadly assessed by comparing concentrations of S with an incompatible trace element that provides an index of fractionation, such as Zr. This logarithmic plot of whole-rock S and Zr concentrations shows that the Arunta intrusions fall into two major geochemical groups that highlight geographical differences in prospectivity. (1) A S-rich group (~300 to 1200 ppm S) from the western and central Arunta that could be prospective for orthomagmatic Ni-Cu-Co sulphide deposits. In particular, the Andrew Young Hills intrusion is the most evolved and contaminated S-rich body investigated, and the Mount Chapple Metamorphics and Mount Hay Granulite bodies represent large S-saturated mafic magmatic systems. (2) A relatively S-poor (< 300 ppm S), slightly more primitive group from the eastern Arunta that is more favourable for orthomagmatic PGE-sulphide deposits. Of this group the Attutra Metagabbro, Riddock Amphibolite, and Mordor Complex have low S concentrations that indicate they are prospective for stratabound and/or hydrothermal PGE mineralisation. Both groups (1) and (2) have some potential for polymetallic deposits of hydrothermal Cu-Au ± PGEs ± Ag ± Pb spatially associated with the intrusions. �

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Vertical gradient of total magnetic intensity of the Andrew Young Hills Intrusion, reduced to pole (processed by T. Meixner, Geoscience Australia). These aeromagnetics indicate a subsurface synclinal body plunging towards the south-southwest and measuring 32 km east-west by 13 km north-south. Irregularities and embayments along the northern arcuate basal contact and possible feeder conduits might be the initial exploration focus for massive Ni-Cu-Co sulphides in this ‘S-bearing’ intrusion.�

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The Avebury Ni deposit near Zeehan on the west coast of Tasmania is an unusual Ni occurrence. This part of western Tasmania is world-renowned for its diversity and size of mineral deposits, several of which are of world-class status. Avebury occurs in a sequence of Cambrian ultramafic intrusives, mafic volcanics, and various sediments, that were intruded by the Devonian-Late Carboniferous Heemskirk Granite in the northwest.�

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Nickel sulphide mineralisation in this concealed deposit occurs near the margin of a serpentinised ultramafic body with abutting sediments. The Ni appears to have been remobilised by heat/fluids associated with the granite intrusion or by serpentinisation of the ultramafic host rock and redeposited in trap sites around the top and margins of the altered body. The mineralisation is mainly coarse-grained pentlandite and magnetite. The mineralising system is S-poor and iron-rich, with variable, but minor pyrrhotite, pyrite, and Ni arsenides. There is little or no associated Au, Cu, or PGEs. A decline has been commissioned as part of a feasibility study for mining. Avebury represents a ‘new’ style of Ni mineralisation and there is potential for the discovery of further deposits in western Tasmania.�

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Significant Ni-Cu intersections/resources associated with komatiites and mafic intrusions over the last two years and potential Archaean-Proterozoic provinces for these magmatic systems are highlighted (colour coded) on the map below.�

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Check list of elements considered important for assessing mineralised komatiites in the Lake Harris, Eastern Goldfields, and Southern Cross provinces.�

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Check list of elements considered important for assessing mineralised mafic intrusions in the Musgrave, Halls Creek, and Pilbara provinces.�

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GIS showing Nickel Metallogenic Provinces in Australia’s Archaean and Proterozoic. Example shown is the Yilgarn Craton, Western Australia. This presentation provides a quick insight into the Ni-sulphide industry of Australia - a very dynamic and exciting environment that is rapidly changing, i.e., regular announcements of new discoveries, intersections, upgraded resources, and new mineralised provinces. Ni-sulphide deposits in Australia are mainly associated with Archaean komatiites and Archaean-Proterozoic mafic intrusions, but some unusual Phanerozoic deposits occur in eastern Australia. The majority of Australia’s Ni production (~80%) is derived from komatiite deposits in the Yilgarn Craton of Western Australia. The Eastern Goldfields Province of this craton hosts one of the greatest concentrations of Archaean komatiite-hosted Ni deposits in the world, several of which are world class (>1 Mt Ni). Exploration activities in Australia are currently focussed on mafic-ultramafic rocks in Late Archaean and Proterozoic provinces. Exploration has been stimulated by the discovery of new deposits (Flying Fox, Daybreak, Armstrong, Daltons, McEwen, Nebo-Babel), recognition of different styles of mineralisation (Avebury), and the protracted period of elevated Ni metal prices. There is considerable potential for finding new deposits associated with komatiites and mafic intrusions, particularly under shallow cover.�

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